Luteal Function in Baboons with Administration of the Antiestrogen Ethamoxytriphetol (MER-25) Throughout the Luteal Phase of the Menstrual Cycle1

Abstract

Administration of the antiestrogen ethamoxytriphetol (MER-25) during late baboon gestation has been reported to result in a marked decline in progesterone (P) production rate. Since both the placenta and corpus luteum appear to secrete P during late baboon gestation, this decline in P may reflect a loss in luteal and/or placental function. Therefore, the present study determined the effect of administration of the antiestrogen MER-25 upon serum steroid concentrations during the luteal phase of the baboon menstrual cycle, a tijne when the source of P is almost exclusively the corpus luteum, Six baboons were bled throughout a control menstrual cycle and during daily administration (15 mg/kg BW, p.o.) of MER25 throughout the luteal phase of the following cycle. Mean (± SEM) length of the luteal phase of the menstrual cycle was the same in baboons with no treatment (18 ± 0 days) and after MER-25 administration (18 ± 0 days). Mean (± SEM) serum concentrations of P were similar in the luteal phase with no treatment (5.2 ± 0.7 ng/ml) and during MER-25 administration (5.0 ± 0.6 ng/ml). Serum P attained similar peak values of concentration in the luteal phase before and after antiestrogen administration and was detectable in the serum for a similar duration of the lutes] phase of both cycles. Mean (± SEM) serum concentrations of 17-hydroxyprogesterone (17-01(P), which may also provide an index of lutes] function, were similar in the luteal phase of the menstrual cycle in baboons with no treatment (0.53 ± 0.20 nglml) and during administration of MER-25 (0.42 ± 0.15 ng/inl). Serum estradiol (E2) concentrations attained a peak at midcycle, then declined to low values, and MER-25 had no effect upon serum E2.